Add possibility to use custom equality comparator in

[bennidi]

I have recently been using the .have.properties() assertion a lot and in all my use cases I needed a value based comparison (deep equals) instead of ===

I would suggest to add an optional parameter to the properties method that will take a custom comparison function. The default value could be an implementation that uses '==='.

This is how it would look in coffeescript (sorry, for being too lazy to translate into ES)

isEqual = (a,b) -> a is b

(props, equals= isEqual) ->
  obj =@actual
  ok = @actual isnt null

  if ok then for key,value of props
      ok = key of obj and equals obj[key], props[key]
      if not ok then break
  @assert(ok, "have properties", {expected: props, diffable: true})